Marijuana use impairs memory, attention, and executive functioning. These impairments increase with long-term use. While several studies have reported residual cognitive impairments within days of abstinence from long-term use, the extent to which marijuana-induced cognitive performance deficits extend further into the abstinence period has received little study. These cognitive deficits may be further confounded by residual impairing effects of marijuana on motivation. That is, cognitive performance deficits during abstinence from heavy marijuana use may be due to impairment of processing ability, diminished motivation to perform well, or both. The goal of this research proposal is to fill these two critical knowledge gaps by quantifying marijuana withdrawal effects on memory and attention. We will repeatedly test memory and attention in marijuana-dependent adults with a heavy use history both before and during withdrawal from chronic marijuana use. A group of former light users will serve as a control group. We will also isolate the role of motivational drive in marijuana-related and withdrawal-related impairments. Monetary incentive for accurate performance will be provided to separate groups of marijuana abstinent adults and control subjects. The key dependent variable will be improvement of performance over repeated testing. Testing during abstinence will coincide with the ascent (day 1), peak (day 3), and descent (days 7 and 21) of the typical withdrawal syndrome. By quantifying cognitive impairment, then dissociating processing deficit from effort expended, the proposed studies will further our understanding of the effects of THC on cognitive performance before and after abstinence.